Multiphase polymers resins

High heat ABS resins described in this chapter refer to a family of multiphase polymers which are dimensionally stable at temperatures where conventional, general-purpose ABS deforms. The maximum end-use temperature at which fabricated parts can meet the functional requirements of the specific application determines whether high heat resistant ABS or conventional ABS will be used. Typical applications for high heat ABS are automotive interior components that can be exposed to temperatures of more than 90 °C. Conventional ABS warps unacceptably in that environment. 

Multiphase polymer blends are often easier to process than a single polymer with similar properties. Blending two or more polymers offers another method of tailoring resins to a specific application. Polymer blends usually have physical and mechanical properties that he between the values of their constituent materials because polymer blends are only a physical nuxture. Additional information on the subject of polymer blends is available in the literature [9-11]. 

As may be guessed from the names for these systems, the rubber particles are added to improve the mechanical properties of the matrix material, particularly to improve their low impact strength. The size of the rubber particles, their distribution, composition and compatability with the matrix all influence the mechanical properties of the final engineering resin. T) ical multiphase polymers which include elastomers... 

Multiphase polymers are commonly toughened plastics which contain a soft, elastomeric or rubbery component in a hard glassy matrix or in a thermoplastic matrix. An example of the typical brittle fracture morphology of an unmodified thermoplastic is shown by SEM of nylon (Fig. 5.45A). Addition of an elastomeric phase modifies the brittle fracture behavior of the matrix, as shown in a fracture surface of a modified nylon (Fig. 5.45B). The modification depends on the composition and deformation mechanism of the material [204, 215], but normally it increases the fracture toughness and strength from that of the unmodified matrix resin. Impact strength, as measured for instance by an Izod impact testing apparatus, is affected by the dispersed phase... 

Although the appliance of the epoxy thermosets is under continuous development, there are still many aspects to be improved. Epoxy resins are not the lowest cost materials available for most of the aforementioned applications. Thus, epoxy resins must provide added value to justify their additional cost. This added value is usually realized by the incorporation of a special property or combination of properties into the final product, which can often be designed through multiphase polymer system mechanisms. 

As in the case of emulsion polymerization, particle morphology is ruled by the interplay between thermodynamics and kinetics. Equilibrium morphologies are reached when the internal viscosity of the polymer particle is low. Thus, due to the plasticizing effect of the alkyd resin, equilibrium morphologies are usually reached for alkyd/acrylic systems [96]. The equilibrium morphology is affected by the presence of graft copolymer that reduces the interfacial tension between the polymer phases in the particle. Methods to calculate the equilibrium morphology of multiphase polymer particles are available [43]. 

This process, which is a maximization of the reactor granule technology, produces a broad range of multiphase polymer alloys directly in the reactor. These polyolefins can compete with other engineering resins such as nylon, PET, ABS, PVC, and even with many high-performance materials such as steel in the automotive sector. 

When analyzing multiphase samples, it may be possible to detect several glass transitions in a DMA measurement as was the case in the thermal characterization of multiphase polymer films described above. DMA is also able to provide information on the effects of plasticizers, resins and fillers on the polymer fihn. 

The world production of plastics in 1995 is projected at 76 million metric tons (mT) with an annual growth rate (AGR) of 3.7%. The expected AGR of PBAs is 12% and that of composites 16%. In 1987, 21% of polymers were used in blends and 29% in composites and filled plastics [56]. If this trend continues, by 1995 all manufactured resins will be used in multiphase polymeric systems. Two factors moderating the tendency are ... 

Scanning electron microscopy (SEM) involves scanning an electron beam (5-lOnm) across a surface and then detecting the scattered electrons. Literature abounds, with work focussing on the use of SEM in the fracture and failure of epoxy resins and other thermoset polymers. Also work on multiphase thermosets (thermoset-thermoplastic blends, thermoset nanocomposites, interpenetrating network (IPN) polymers) is abundant. 

Block polymers and polymer blends deserve now a great intere because of their multiphase character and their related properties. The thermodynamic immiscibility of the polymeric partners gives rise indeed to a phase separation, the extent of which controls the detailed morphology of the solid and ultimately its mechanical behavior. The advent of thermoplastic elastomers and high impact resins (HIPS or ABS type) illustrates the importance of the industrial developments that this type of materials can provide. In selective solvents, and depending on molecular structure, concentration and temperature, block polymers form micelles which influence the rheological behavior and control the morphology of the material. 

Polymers in the category of engineering resins and plastics may be classified in several ways. They may be thermoplastic or thermoset. They may be crystalline or amorphous and they may be single phase or multiphase systems. This would allow for eight types of materials except that thermosets, because of their irregular cross-linked structure, are never crystalline. Single phase polymers do not have discemable second phase structures of different chemical composition. Thus homopolymers and random copolymers are single phase polymers, even if they are semicrystalline and so contain amorphous and... 

From the experimental results obtained, it was concluded that the synthetic hinders were thermorheologically complex materials as a consequence of the formation of a multiphase system. In fact, their mechanical behaviour is different according to the range of temperatures studied. While at low temperatures the binder mimics the mechanical properties of the oil-resin phase, at high temperatures the mechanical behaviour of the binder seems to be due to the polymer. Finally, the complex viscosity of these blends can be predicted using a logarithmic mixing rule, as will be discussed later. 

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